Calculate the percentage composition of each compound. a) Ammonium nitrate b) Aluminum sulfate c

Calculate the percentage composition of each compound. a)...

Key Concepts

Atomic Weights

Atomic weights are the weighted averages of the masses of the isotopes of an element as they naturally occur. These values, typically found on the periodic table, are used in calculating the molar mass of compounds and are essential for performing accurate stoichiometric computations in chemistry.

Chemical Formula

A chemical formula represents the types and numbers of atoms in a compound. It is fundamental to understanding a compound’s composition and structure, and it forms the basis for calculating its molar mass and percentage composition. The subscript numbers in the formula indicate the proportion of each atom in the molecule.

Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in chemical reactions. In the context of percentage composition, stoichiometry is used to relate the number of atoms of each element in a compound to the overall mass of the compound, ensuring that the calculated percentages correctly reflect the compound's elemental makeup.

Percentage Composition

Percentage composition refers to the fraction by mass of each element present in a given compound, expressed as a percentage of the total molecular or formula mass. This concept is used to determine how much of each element is present in a compound, which is crucial for tasks such as determining empirical formulas and for industrial applications, quality control, and chemical analysis.

Molar Mass

Molar mass is the mass of one mole of a substance and is calculated as the sum of the atomic masses of all the atoms in its chemical formula. It provides a bridge between the microscopic scale (individual atoms and molecules) and the macroscopic scale (bulk measurements), and it is essential for converting between mass and moles in chemical calculations.

Transcript

00:01 Hi there.

00:02 This problem is going to be a little bit of a lengthy problem because it does have five parts to it, but in each part we are finding percentage composition.

00:11 So what we're going to need to do for each question is first determine the formula of the compound.

00:17 Then we're going to add the masses together for each element to determine the total molar mass for the compound.

00:25 We're going to get those molar masses from the periodic table.

00:29 And then we're going to divide the individual masses of each element in the compound by that total mass to give us percentage composition.

00:38 So let's go ahead and get started with letter a.

00:41 In letter a, we are given ammonium nitrate.

00:45 Ammonium is nh4.

00:48 It's a polyatomic ion with a plus one charge.

00:53 And nitrate, which is another polyatomic ion with a one negative charge.

00:59 This is the correct formula for ammonium nitrate.

01:01 We can see that because positive 1 and negative 1 adds up to 0.

01:06 All right.

01:06 Next thing we need to do is to determine the total molar mass of this compound.

01:11 So i'm going to list out my elements.

01:14 This compound contains nitrogen, it contains hydrogen, and it contains oxygen.

01:22 For the nitrogen, we see one nitrogen in ammonium and one nitrogen in the nitrate for a total of two nitrates.

01:29 I'm going to look at nitrogen on the periodic table and see that its mass is 14 .01 grams per mole.

01:41 Hydrogen, there are a total of four hydrogens in this formula.

01:48 Looking at the periodic table, hydrogen's mass is 1 .008 grams per mole.

01:54 And for oxygen, we have three oxygens with each oxygen being 16 .00 grams.

02:00 Let me go ahead and multiply these out.

02:04 So 2 times 14 .01 gives me 28 .02.

02:13 I get 4 .032 and i get 48 .00.

02:22 So these are the individual masses.

02:26 These are grams for each of the elements in this compound.

02:30 Adding these together gives me the total mass for the compound.

02:35 So when i add these together, i get 80 .052 grams.

02:44 So of this 80 .052 grams, 28 .02 grams is due to the nitrogen.

02:50 4 .032 grams is due to the hydrogen, and 48 grams is due to the oxygen.

02:56 To calculate percentage composition, i'm going to figure out the percent that each of these masses are of the total percent.

03:04 So here we go.

03:05 For nitrogen, 28 .02 grams of the total 80 .052.

03:16 Going to do this division, i'm going to multiply by 100 to change this to a percent, and i find that the percent of nitrogen in this compound is 35 percent.

03:33 Repeating this process for the hydrogen, 4 .032, divided by the total mass, multiply by 100 % will give me 5 .04 % of the hydrogen.

03:58 And finally, for the oxygen, 48 grams are due to the oxygen, divided by the total mass of 80 .052 grams, gives me a mass of 59, or i'm sorry, gives me a percent, rather.

04:19 I'm multiplied by 100 to give me a percent.

04:21 That's going to give me 59 .96%.

04:27 A great way to check your work on these percentage composition problems is to make sure that your percentages add up to 100, the total percent of the compound.

04:40 Confirming that these, in fact, do i have my answer for part a of this problem.

04:47 35 % nitrogen, 5 .04 % hydrogen, and 59 .96 % oxygen.

04:55 Moving on to part b.

04:57 In part b, we have aluminum sulfate.

05:10 Writing the formula correctly gives me al2, so4 in parentheses, 3.

05:18 That is because aluminum's charge is 3 plus, and sulfate, the polyatomic ion, is 2 minus.

05:25 So to make these charges add up to zero, i have to add a subscript of 2 on the aluminum, and a 3 on the sulfate.

05:31 All right, now we are ready to start determining our percentage composition.

05:38 So as before, i'm going to list out the elements found in this compound.

05:45 There's two aluminum times the mass of aluminum, which is 26 .98.

05:54 Multiplying these together, two times 26 .98 gives me 53 .96 grams.

06:04 For the sulfur, there's only one sulfur.

06:09 Mass from the periodic table is 32 .07 grams.

06:18 So 32 .07 grams from the sulfur.

06:22 And then we have the oxygen.

06:24 There are 12 oxygen in that formula.

06:26 Three times four gives me 12 oxygen at 16 grams each.

06:33 That is going to be 192 grams.

06:40 All right.

06:42 Adding these together, i get the total mass of this compound as 278 .03 grams.

06:55 Now i'm ready to find percentage composition.

06:58 Remember to find percentage composition for each element.

07:02 We're going to take the mass of the element and divide it by the total mass.

07:07 So for aluminum, when i take 53 .96 and divide it by 278 .03, i'm going to get 19 .4 % for the aluminum.

07:24 For the sulfur, i'm going to take the 32 .07 and divide that by 278 .03.

07:35 I'm going to express that as a percent by multiplying my answer by 100, and i find that i have 11 .5 percent sulfur.

07:47 Finally, the oxygen.

07:49 To find the oxygen, i'm going to take oxygen's mass and divide that by the total mass.

07:57 So, 192 divided by 278 .03, multiply it by 100 percent to express it as a percentage, and i'm going to get 69 .1 % oxygen.

08:12 I want to go ahead and check my work.

08:14 Make sure these add up to 100.

08:17 It appears that they do.

08:19 So that's a good sign.

08:23 And this is my answer for percentage composition for part b.

08:29 All right, moving on to part c.

08:32 We should be getting the drill here.

08:34 We need the formula first for ammonium carbonate.

08:38 Ammonium is nh4 with a one plus charge and carbonate is negative two.

08:45 So i'm going to need two of the ammoniums for one carbonate.

08:50 This particular compound has four elements in it, but we're still going to figure out the percentage composition exactly the same way.

09:00 We're going to have to add the individual masses together for each element to get our total mass, and then we will divide the individual mass of each one by the total mass to give us percentage.

09:13 So starting with nitrogen, there are two nitrogens, each of those, 14 .01 grams from the periodic table.

09:21 Hydrogen, two times four gives me eight hydrogens, 1 .008 grams from the periodic table.

09:29 Carbon, there's only one carbon, 12 .01.

09:35 And the oxygen, there are three of those.

09:41 The oxygen is 16 .000...

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